Conducting device, in particular corrugated fin, for a heat exchanger

ABSTRACT

The invention relates to a conducting device, in particular a corrugated fin, for a heat exchanger, having at least one surface. In order to improve the efficiency of heat exchangers, in particular of evaporators, the surface of the conducting device has an increased roughness, in particular microscopic roughness.

The invention relates to a conducting device, in particular a corrugatedfin, for a heat exchanger, with at least one surface. The invention alsorelates to a method for increasing the roughness, in particular themicroscopic roughness, of the surface of a conducting device of thistype. The invention furthermore relates to a heat exchanger, inparticular an evaporator for an air-conditioning system of a motorvehicle, with tubes through which a medium flows and between whichconducting devices are arranged, said conducting devices having afurther medium, in particular moist air, flowing around them.

The heat transfer capacity of evaporators in motor vehicles isdetermined, inter alia, by the condensation of the air moisture on theevaporator surface. In order to obtain an optimum transfer of heat, thecondensed water on the evaporator surface should not form any drops, butrather must drain off as a uniform film. German utility model DE 201 19741 U1 discloses a heat transfer surface on tubular or plate-like bodieswith a microstructure, which projects out of the basic surface, ofprojections which are galvanized onto the basic surface at a minimumheight of 10 μm. The basic surface is entirely or partially covered byprojections. The projections are applied in the form of orderlymicrostructures and are in the shape of pins. German laid-openspecification DE 102 39 071 A1 discloses a method for producing surfaceson which liquids do not adhere. The known surface has a multiplicity ofdepressions or elevations.

It is the object of the invention to improve the efficiency of heatexchangers, in particular of evaporators.

The object is achieved in the case of a conducting device, in particulara corrugated fin, for a heat exchanger, with at least one surface, inthat the surface of the conducting device has an increased roughness, inparticular microscopic roughness. By means of the specific increase inthe roughness on the surface of the conducting device, the condensationof moisture on the surface of the conducting device is evened out andthe drainage of water improved. As a result, the transfer capacity of aheat exchanger equipped with the conducting device can be increased.

A preferred exemplary embodiment of the conducting device ischaracterized in that particles which have a size from 10 to 80 μm arearranged on the surface of the conducting device. The particles arepreferably of platelet-like, globular or needle-like design.

A further preferred exemplary embodiment of the conducting device ischaracterized in that the particles or some of the particles are formedfrom a metallic material. The particles are preferably formed from thesame material or a similar material as the conducting device. As aresult, the production and the recycling of a heat exchanger equippedwith the conducting device are facilitated.

A further preferred exemplary embodiment of the conducting device ischaracterized in that the particles or some of the particles are formedfrom pure aluminum. Within the context of the present invention, goodresults have been obtained with pure aluminum.

A further preferred exemplary embodiment of the conducting device ischaracterized in that the particles or some of the particles are formedfrom a non-metallic material. The non-metallic material preferably hashydrophilic properties.

A further preferred exemplary embodiment of the conducting device ischaracterized in that the non-metallic material is selected from thegroup comprising oxides, nitrides, carbides and borides of the elementsof the third, fourth and fifth transition group and of the third andfourth main group of the periodic table of the elements.

A further preferred exemplary embodiment of the conducting device ischaracterized in that the particles or some of the particles are formedfrom titanium dioxide (TiO₂). Within the context of the presentinvention, good results have been obtained with titanium dioxide.

In the case of a method for increasing the roughness, in particular themicroscopic roughness, of at least one surface of a conducting device,in particular a corrugated fin, for a heat exchanger, the previouslystated object is achieved in that particles are added to a flux, saidparticles being applied together with the flux to the surface of theconducting device or of a semi-finished conducting device. The flux ispreferably a flux based on a potassium fluoroaluminate with the totalformula K₁₋₃AlF₄₋₆. Use is preferably made of a flux which is sold underthe name Nocolok® by Solvay.

A preferred exemplary embodiment of the method is characterized in thatthe flux is applied together with the particles in the form of asuspension to the surface of the conducting device or of a semi-finishedconducting device. The preferably aqueous suspension contains a bindingagent. The binding agent ensures, inter alia, that the particles adhereto the surface of the conducting device or of the semi-finishedconducting device.

A further preferred exemplary embodiment of the method is characterizedin that the flux is applied together with the particles to a corrugatedfin strip. The application can take place before or after punching ofthe corrugated fin strip. The corrugated fin strip is preferably in theform of “coils”. The application method is therefore also referred to ascoil coating.

A further preferred exemplary embodiment of the method is characterizedin that the flux is applied together with the particles by spraying ordip-coating onto the surface of the conducting device or of asemi-finished conducting device. These application methods have provenadvantageous in the context of the present invention.

Further preferred exemplary embodiments of the method are characterizedin that the surface is roughened by slight chemical etching and/or bymechanical machining, such as brushing, grinding or abrasive-blasting.

A further preferred exemplary embodiment of the method is characterizedin that the particles are applied to the surface of the conductingdevice by thermal metal spraying. The metal particles which are sprayedon are preferably formed from aluminum or an aluminum alloy.

The invention also relates to a heat exchanger, in particular anevaporator for an air-conditioning system of a motor vehicle, with tubesthrough which a medium flows and between which previously describedconducting devices are arranged, said conducting devices having afurther medium, in particular moist air, flowing around them. Theroughness of the surfaces of the conducting devices has preferably beenincreased by a previously described method.

Further advantages, features and details of the invention emerge fromthe description below in which various exemplary embodiments aredescribed in detail. The features mentioned in the claims and in thedescription may in each case be essential here to the inventionindividually by themselves or in any desired combination.

The invention relates in particular to evaporators of motor vehicleair-conditioning systems. An evaporator of this type is arranged, forexample, in the passenger compartment of the motor vehicle. A fan sucksup air from the outside or in the passenger compartment and delivers itvia the evaporator. In the process, the air is cooled and excess airmoisture present is precipitated. The condensation water is collectedbelow the evaporator and conducted away to the outside via a conduit.The evaporator comprises a multiplicity of tubes through whichrefrigerant flows. Conducting devices, in particular corrugated fins,are arranged between the tubes and have the moist air flowing aroundthem.

The conducting device is a corrugated fin which is present in the formof a corrugated fin strip on a “coil”. According to an essential aspectof the present invention, the microscopic roughness of the corrugatedfin is increased in a specific manner. The microscopic roughness of thecorrugated fin can be increased before or after punching of thecorrugated fin.

The corrugated fin is coated with a flux. The flux is a flux based onpotassium fluoroaluminate with the total formula K₁₋₃AlF₄₋₆. Such a fluxis sold under the name Nocolok® by Solvay.

According to one embodiment of the invention, metallic particles areadded to the flux. The metallic particles are formed from pure aluminumand have a grain size of between 10 and 80 μm.

According to a further embodiment of the invention, non-metallicparticles with a grain size of between 10 and 80 μm are added to theflux. The non-metallic particles are preferably formed from titaniumdioxide (TiO₂).

According to a further embodiment of the invention, the particles areapplied by thermal spraying of metals. Aluminum or aluminum alloys is orare used as the spraying material. The method parameters in the case ofmetal spraying are selected in such a manner that the metal particlesproduced are of a size of between 10 and 80 μm.

The flux together with the metallic or non-metallic additives ispreferably applied by means of coil coating. As an alternative, thesuspension containing the flux and the additives can also be applied byspraying or dip-coating.

According to a further embodiment of the invention, the surface of thecorrugated fins is roughened by slight chemical etching. As analternative or in addition, the corrugated fin surface can also bemechanically roughened by brushing, grinding or abrasive-blasting. It isalso possible to subsequently coat the corrugated fin surface withorganic polymers to which metallic or non-metallic particles are added.

The addition of the particles to the flux has the advantage that themodification of the corrugated fin surface in order to increase themicroscopic roughness can take place in-line during a soldering process,without additional re-coating. The heat transfer between the heatexchanger surface and the air is improved by increasing the microscopicroughness. As a result, the transfer capacity of the heat exchanger canbe increased. The condensation of moisture on the corrugated fin issignificantly improved by increasing the microscopic roughness of thecorrugated fin surface. Furthermore, the water drainage of an evaporatorequipped with the corrugated fins according to the invention isimproved. As a result, the overall size of the evaporators can bereduced while maintaining the same heat transfer capacity. As analternative, the heat transfer capacity can be increased whilemaintaining the same overall size.

1. A conducting device, in particular corrugated fin, for a heatexchanger, with at least one surface, wherein the surface of theconducting device has an increased roughness, in particular microscopicroughness.
 2. The conducting device as claimed in claim 1, whereinparticles which have a size of from 10 to 80 μm are arranged on thesurface of the conducting device.
 3. The conducting device as claimed inclaim 1, wherein the particles or some of the particles are formed froma metallic material.
 4. The conducting device as claimed in claim 3,wherein the particles or some of the particles are formed from purealuminum.
 5. The conducting device as claimed in claim 1, wherein theparticles or some of the particles are formed from a non-metallicmaterial.
 6. The conducting device as claimed in claim 5, wherein thenon-metallic material is selected from the group comprising oxides,nitrides, carbides and borides of the elements of the third, fourth andfifth transition group and of the third and fourth main group of theperiodic table of the elements.
 7. The conducting device as claimed inclaim 1, wherein the particles or some of the particles are formed fromtitanium dioxide (TiO₂).
 8. A method for increasing the roughness, inparticular the microscopic roughness, of at least one surface of aconducting device, in particular a corrugated fin, for a heat exchanger,in particular as claimed in claim 1, wherein particles are added to aflux, said particles being applied together with the flux to the surfaceof the conducting device or of a semi-finished conducting device.
 9. Themethod as claimed in claim 8, wherein the flux is applied together withthe particles in the form of a suspension to the surface of theconducting device or of a semi-finished conducting device.
 10. Themethod as claimed in claim 8, wherein the flux is applied together withthe particles to a corrugated fin strip.
 11. The method as claimed inclaim 8, wherein the flux is applied together with the particles byspraying or dip-coating onto the surface of the conducting device or ofa semi-finished conducting device.
 12. A method for increasing theroughness, in particular the microscopic roughness, of at least onesurface of a conducting device, in particular a corrugated fin, for aheat exchanger, in particular as claimed in claim 1, wherein the surfaceis roughened by slight chemical etching.
 13. A method for increasing theroughness, in particular the microscopic roughness, of at least onesurface of a conducting device, in particular a corrugated fin, for aheat exchanger, in particular as claimed in claim 1, wherein the surfaceis roughened by mechanical machining, such as brushing, grinding orabrasive-blasting.
 14. A method for increasing the roughness, inparticular the microscopic roughness, of at least one surface of aconducting device, in particular a corrugated fin, for a heat exchanger,in particular as claimed in claim 1, wherein the particles are appliedto the surface of the conducting device by thermal metal spraying.
 15. Aheat exchanger, in particular evaporator for an air-conditioning systemof a motor vehicle, with tubes through which a medium flows and betweenwhich conducting devices as claimed in claim 1 are arranged, saidconducting devices having a further medium, in particular moist air,flowing around them.